Which parameter is crucial when fitting multifocal lenses?

When fitting multifocal lenses, the lower edge of lens placement is a critical parameter. This is because the design of multifocal lenses includes various zones for different vision needs, such as distance, intermediate, and near vision. The lower edge placement determines how effectively the wearer can transition between these zones. If the lenses are positioned too low or too high relative to the pupil, it can affect the visual performance, making it difficult for the user to see clearly at different distances.

Proper alignment of the lower edge ensures that the different optical zones align correctly with the wearer's line of sight. When the lower edge is positioned correctly, the wearer can comfortably look through the lens areas designed for near vision when reading or engaging in close-up tasks, while still having access to the distance vision portion of the lens above.

While other parameters, such as pupil distance, frame width, and lens color, can influence lens fitting and comfort, they do not have the same direct impact on the functionality of the various zones in multifocal lenses as the lower edge placement does. For example, pupil distance primarily ensures that the optical centers of the lenses align with the wearer's pupils, which is certainly important but secondary to the functioning of the multifocal design itself. Frame width can affect